HRVSpark vs Sleep Tracker
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
HRVSpark
Visualize your raw heart rate variability data directly on your Apple Watch face with a dynamic sparkline complication. Get immediate insights into your body's trends without opaque scores or labels. A companion iPhone app provides detailed views and guidance.
- Raw HRV sparkline complication
- 8-hour free complication
- 24/7, 7-day, 30-day Pro views
- Circular gauge and corner complications
- iPhone companion app
- No interpretation layer
- Complication-first design
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HRVSpark puts your heart rate variability on your Apple Watch face as a sparkline, a gauge, or a corner complication. It shows the SDNN readings saved in Apple Health and nothing more. WHAT YOU GET • Three free 8-hour complications: a sparkline, a gauge, and a corner • Seven Pro complications across 24-hour, 7-day, and 30-day windows • Gaps left visible when your watch took no readings • An iPhone app with a live gallery of every complication and setup help JUST YOUR HRV HRVSpark shows your SDNN values across useful time windows without turning them into a readiness, stress, or recovery score. What they mean for your day is up to you. BUILT FOR THE WATCH FACE The complications are designed for quick checks on the wrist. Each gauge places a recent value between the low and high of its window. The Apple Watch app works without the iPhone app and keeps a record of your daily averages. The iPhone app adds older days whenever you open it. ONE-TIME PRO UNLOCK Download free and use the three 8-hour complications. Unlock all ten with a single one-time purchase. No subscription, account, ads, or telemetry. PAIR IT WITH RHRSPARK RHRSpark gives the same direct view of resting heart rate, with recent sedentary heart rate and Apple's daily resting heart rate. HealthKit data stays on your devices and moves only between your iPhone and Apple Watch through Apple frameworks. HRVSpark may request a small configuration file from filamentlabs.io to show current product messages. That request contains no health data. If you claim the supporter thank-you, HRVSpark sends Apple's signed record of your HRVSpark purchase to filamentlabs.io so each purchase receives one RHRSpark Pro code. That record contains no health data. HRVSpark is for informational purposes only. It does not provide medical advice or diagnose, treat, cure, or prevent any medical condition.
Sleep Tracker
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Understand your signals. Shape your day around them. Cernidia helps you make sense of your sleep, recovery and daily energy, so everyday choices about rest, movement and focus have more context. See the bigger picture behind your numbers and notice patterns over time. No ads, subscriptions or in-app purchases. No Cernidia account needed. UNDERSTAND YOUR SIGNALS • Review your sleep and your next planned sleep window. • Follow your daily energy estimate and recovery in your personal context. • Explore breathing-rate trends, blood-oxygen readings and heart-rate zones when suitable data is available. • Add a quick check-in to record how you feel. CONNECT YOUR WEARABLES Use Apple Health with Apple Watch, or connect an existing WHOOP account. WHOOP Recovery, Sleep, Strain and Workouts are labelled separately. Connections are optional, and Cernidia remains usable without a wearable. PUT INSIGHTS INTO YOUR DAY Give tasks, routines and recovery time a place in your day. Optional calendar access helps your plans fit around real commitments. The Apple Watch companion shows your current and next activity, lets you record an energy check-in and adds heart-rate context to workouts you start. CHOOSE YOUR WAKE-UP WINDOW Smart Wake lets you choose a wake-up window and uses previously recorded sleep phases to estimate a wake time. Your latest wake time serves as a backup. Alarm or notification permissions are needed for alerts; Smart Wake does not detect your current sleep stage in real time. PRIVATE AND OPTIONAL Your health summaries, check-ins and plans stay on your devices. Cernidia has no app-data cloud sync, product analytics, advertising or cross-app tracking. The optional WHOOP connection uses an online authorization service. WHOOP health records are fetched directly to your iPhone and stored locally. WHAT TO EXPECT Personal comparisons need enough readable history. Missing data stays unknown. Features depend on your device, permissions and available records. Apple Watch and WHOOP devices are sold separately; WHOOP also requires its own membership. Cernidia supports general wellness and everyday decisions. It does not diagnose conditions or provide medical treatment recommendations.
Screenshots
Verdict
The clearest difference is in-app purchases: Sleep Tracker at none against HRVSpark's 2. On price, update cadence, ads and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. HRVSpark sells 2 one-off in-app purchases. Sleep Tracker asks for nothing beyond the download.
HRVSpark ships an update weekly, Sleep Tracker every 6 days. The most recent releases landed on October 14, 2026 and October 16, 2026 respectively.
| Parameter | HRVSpark | Sleep Tracker |
|---|---|---|
| Price | Free | Free |
| Rating | 5.0 (2 ratings) — better | — |
| Positive reviews | 100.0% of reviews | — |
| Number of ratings | 2 — better | — |
| Update frequency | Weekly | Every 6 days — better |
| Ads | No | No |
| In-app purchases | Yes | No — better |
| Monetization | Freemium | — |
| Devices | iPhone, iPad, Apple Watch — better | iPhone, Apple Watch |
| Requires iOS | 17.0 — better | 18.0 |
| Further details — not scored | ||
| Size | 6 MB | 24 MB |
| Age rating | 4+ | 4+ |
| Developer | Joel Farthing | Sven Kraln |
In-app purchases
HRVSpark
- HRVSpark Pro$0.99
- HRVSpark Tip Jar$4.99
Sleep Tracker
No in-app purchases









